1. Technical Field
The present invention relates to alternating pressure support surfaces. In particular, it relates to alternating pressure specialty mattresses that provide pressure to only a portion of a body's surface at a time by dynamically varying pressure in discrete compartmented cells of the mattress.
2. Background Art
There are innumerable illnesses and injuries that result in the need for extended bed rest by patients and invalids. Unfortunately, while bed rest is often used to facilitate a patient's recovery from illnesses or injuries, an excessive amount of time spent in bed rest often creates other medical problems. In particular, extended bed rest can result in pressure wounds such as decubitus ulcers or bed sores. The pressure wounds are caused by the reduction in blood flow at a particular point on the patient's body. Usually, this is due to excessive pressure at that point which is caused by continuous uneven support provided by the mattress or support surface which the patient is laying on. As the blood flow is cut off, sores can quickly develop and extend at a rapid pace. If not promptly and properly treated, pressure wounds can even result in a greater injury to a patient than the original illness or injury for which the bed rest was taken. As a result, it would be desirable to have a method of eliminating, or reducing the possibility of getting, pressure wounds when a patient is confined to bed rest.
An early attempt to address this problem was initiated by medical practitioners who would attempt to prevent the occurrence of pressure wounds by physically rotating a patient on the patient's bed on a periodic basis. Due to the shortage of personnel at many medical facilities, or to oversight, manual rotation of patients may not always occur at the proper time. Sometimes, it may not occur at all. As a result, even in a facility where the staff is trained and aware of the problems associated with pressure wounds, patients may not receive adequate care in regard to the avoidance of pressure wounds. It would be desirable to have a method of avoiding the need to rely on human action and to automatically avoid pressure wound injuries caused by constant pressure applied to particular areas of a patient's body.
Another attempt to avoid pressure wounds has been the development of a particular type of specialty mattress that is commonly known as a support surface. This type of mattress attempts to avoid pressure wounds by reducing pressure on the mattress surface through the use of air, gel, or foam. The air, gel or foam based support surfaces are designed to avoid pressure wounds by distributing the patient's weight across a large surface area, which in turn reduces the pressure per square inch and subsequently provides less restriction on patient blood flow. While providing superior performance over conventional mattresses, the specialty mattresses cannot provide a complete answer to the problem of restricted blood flow due to the constant pressure applied against the surface of a patient's body.
An attempt to address this problem has resulted in the development of alternating pressure support surfaces. Support surfaces, which utilize alternating pressure, are used to prevent and cure pressure wounds such as decubitus ulcers and bed sores. In theory, when a patient is placed on this specialty mattress, only one half of the patient's body has pressure on it at any given time. This is accomplished by inflating one set of cells while a second set of cells is deflated. The inflated cells support the weight of the body while the deflated cells do not provide pressure on the patient's body. As a result, the deflated cells provide pressure relief and thereby encourage blood flow. Alternating pressure support surfaces typically use a preset time interval to alternate pressure within the cells. This time interval is typically around five minutes. At the end of the preset time interval, the inflated cells will deflate as the deflated cells inflate. This continually changes the pressure points on the body, allowing blood to flow more freely. The improved blood flow helps to prevent pressure wounds from occurring, and also helps pre-existing wounds to be healed.
While alternating pressure support surfaces improved over the prior art, they have serious drawbacks in that they often are not able to consistently reduce pressure to the proper level and control pressure at the proper levels for the purposes of encouraging blood flow and avoiding pressure wounds. In particular, unless the deflating air cells reach zero or almost zero pressure (2-3 mmHg) inside the air cell, there can still be too much pressure on the patient's body. In fact, the amount of residual pressure can still be enough to break down the patient's skin. Further, even when the air pressure inside the air cell is at zero, there is still pressure on patient's skin that is known as interface pressure. Interface pressure results from the added pressure from coverlets, sheets, bed clothing, etc. It is typically in the range of 3-10 mmHg greater than the pressure inside the air cell. As a result, these prior art systems often fail to prevent pressure wounds because the combination of inaccurate air pressure and interface pressure results in a residual pressure against the skin which is significant enough to inhibit blood flow. It would be desirable to have a system capable of accurately maintaining the desired air pressures inside the air cell such that areas on the surface of a patient periodically have very low interface pressure (zero pressure in the air cell), and a system which is also capable of measuring air cell pressures and adjusting air pressures to account for them.
Another problem associated with prior art alternating pressure support surfaces is that they do not properly control cross over pressures. Cross over pressure is the pressure at which the pressure inside the deflating air cells equals the pressure inside the inflating air cells. Improperly controlled cross over pressure can also contribute to pressure wounds. In particular, if the cross over pressure is too high, then the air cells are over inflated to the point where pressure is applied to the entire surface of the patient's body which means that the patient's body does not receive the benefit of the reduced pressure which would have resulted in increased blood flow. Likewise, if the cross over pressure is too low, then a condition known as bottoming out occurs. Bottoming out is a condition where insufficient air pressure under the patient allows the patient's body to come in contact with the bed frame, resulting in constant pressure against the patient's body. This has the same effect as cross over pressure which is too high. Namely, pressure is applied by the support substrate to the entire surface of the patient which acts to restrict blood flow. It would be desirable to have a system capable of maintaining the cross over pressure point such that it is not too high or too low, thereby preventing pressure from being applied to the patient's entire body surface.
While attempting to address the basic need to prevent the formation of pressure wounds during the healing process, the prior art has failed to provide an alternating pressure support surface that is capable of dynamically measuring and controlling pump pressure, which is capable of dynamically measuring and adjusting pressure to account for air cell pressure, and dynamically measuring and controlling cross over pressure to prevent both over inflation and bottoming out.